Various medical imaging techniques exist to aid clinicians in the diagnosis of pathological conditions caused, for example, by anatomic or functional manifestations of a disease. Many such techniques produce one or more image frames that can be used to highlight to the clinician various instantaneous or temporal variations in anatomical and/or functional properties of a patient.
For example, PET imaging may be used to obtain a sequence of image frames showing, for example, how the physiological functional properties of a patient's organs, such as, for example, the brain, vary over time. See, e.g., S. R. Cherry, J. A. Sorenson, M. E. Phelps, Physics in Nuclear Medicine (3rd Edition), W.B. Saunders Co., ISBN-10: 072168341X, ISBN-13: 9780721683416, August 2003
PET is a known imaging technique that uses tomography to computer-generate a two- or three-dimensional image or map of a functional process in the body as a result of detecting gamma rays when artificially introduced radionuclides incorporated into biochemical substances decay and release positrons. Analysis of the photons detected from the annihilation of these positrons is used to generate the tomographic image frames which may be quantified using a colour scale to show the diffusion of the biochemical substances in the tissue thereby indicating localization of metabolic and/or physiological processes.
For example, radionuclides used in PET may be a short-lived radioactive isotopes such as flourine-18, oxygen-15, nitrogen-13, and carbon-11 (with half-lives ranging from about 110 minutes to about 20 minutes). The radionuclides may be incorporated into biochemical tracer substances such as compounds normally used by the body that may include, for example, sugars, water, and/or ammonia. The tracers may then be injected or inhaled into the body (e.g. into the blood stream) where the substance (e.g. a sugar) becomes concentrated in the tissue of interest, and where the radionuclides decay by emitting positrons. These positrons collide with nearby electrons producing gamma ray photons which can be detected and recorded thereby indicating where the radionuclide was taken up by the body. This set of data may be used to explore and depict one or more of anatomical, physiological, and metabolic information in the human body.
Although many tracers are currently used in PET studies to good effect, where various different tracers are used, e.g. for comparative studies of the same anatomical region, their differing biochemical properties can give rise to false indications of metabolic information for a particular organ.
For example, two different tracers might have different binding properties in a particular organ, respectively favoring binding to different tissue types. Additionally, or alternatively, different tracers might have different permeation rates across a particular membrane, such as the blood-brain boundary (BBB), for example.
Hence, when using various tracers, data analysis is more difficult and clinicians' attention might not be accurately drawn to the most clinically important organs, or regions of organs, since, for example, tissues or vessels surrounding them may show a higher tracer uptake than those more clinically significant areas.
There therefore exists a need for an improved imaging technique in which the most clinically significant features can be more reliably extracted for highlighting to clinicians, for example.